Turbine blade with bracket in tip region

ABSTRACT

A turbine blade is provided with a bracket arranged in the tip region of the blade and projecting beyond the blade profile. The bracket is formed merely in a section of a surface region of the pressure side, the surface region being enclosed by an imaginary chord bearing against the pressure side of the blade body both in the region of the leading edge and in the region of the trailing edge.

FIELD OF THE INVENTION

The invention relates to a turbine blade having a bracket arranged inthe tip region of the blade and projecting beyond the blade profile.

BACKGROUND OF THE INVENTION

In particular in smaller turbomachines, the gap losses occurring in thetip region of the turbine blades, i.e. between the blade tip and theblade shroud, may assume considerable proportions and thus may lead to adistinct loss of efficiency. These gap losses are caused by the pressuredifference between the pressure side and the suction side in the tipregion of the blade, as a result of which there is an overflow of theworking fluid. This overflow can be reduced by increasing the frictionlosses between the blade tip and the blade shroud, a factor which leadsto a reduction in the gap losses and thus to an increase in theefficiency.

A known measure aimed at reducing the gap losses and increasing thereliability of the turbine blade is the arrangement of a rib or bracket(so-called minishroud or winglet) projecting laterally beyond the bladeprofile in the tip region of the blade (Ü. Okapuu, presentation“Aerodynamic design of first stage turbines for small aero engines”,held as part of the lecture series 1987-07 of the Karman Institute forFluid Dynamics, on the topic “Small High Pressure Ratio Turbines”, Jun.15-18, 1987, pages 1-4 and FIGS. 1-4). GB-A-2 153 447 and GB-A-2 050 530also disclose blade bodies having brackets projecting onto the suctionside and onto the pressure side. GB-A-2 050 530 also indicates a bladebody having a bracket which is arranged on the suction side and abovewhich the blade body rises on all sides.

However, all these solutions result in an increase in both the leadingand trailing wedge angles of the blade and thus in correspondingefficiency losses.

SUMMARY OF THE INVENTION

The object of the invention, in attempting to avoid all thesedisadvantages, is to achieve a further improvement in efficiency for aturbine blade which is provided with a bracket arranged in the tipregion of the blade and projecting beyond the blade profile.

According to the invention, this is achieved in that, the bracket isformed on the pressure side of the blade and only in a section of adefined surface region of this pressure side. In this case, this definedsurface region constitutes that region of the pressure side which isenclosed by an imaginary chord bearing against the pressure side of theblade body both in the region of the leading edge and in the region ofthe trailing edge.

The pressure-side section having the bracket is formed between and at adistance from two points lying on the pressure side of the blade body,the first point being arranged in the region of the leading edge and thesecond point being arranged in the region of the trailing edge, and theimaginary chord bearing against both points. It has proved to beespecially expedient to form a distance a₁, a₂ between the first pointand the bracket and between the second point and the bracket, and thisdistance a₁, a₂ in each case corresponds approximately to a bladethickness d₁, d₂ in the corresponding region of the blade body.

Since the bracket therefore extends only over part of the pressure side,both wedge angles of the blade body, i.e. the leading angle and thetrailing angle, can be kept small. The wedge angles can be reducedfurther through selection of the defined distances a₁, a₂. This resultsin an acute blade geometry, which ensures that high Mach numbers in theleading-edge region and wake zones in the trailing-edge region of theblade body are avoided. Ultimately, a further improvement in efficiencyis achieved while a reduction in the gap losses continues to be ensured.

Starting from the leading edge, the bracket has a maximum height h_(max)above the pressure side in a region of 30 to 40% of the chord length lof the blade body. In this case, the height of the bracket continuouslydecreases both in the direction of the leading edge and in the directionof the trailing edge of the blade body. The maximum height h_(max) ofthe bracket corresponds approximately to a blade thickness d₃ as formedin a region of the blade body which is adjacent to the bracket andremote from the blade tip. Furthermore, it is advantageous if thebracket is of wavelike design.

It has been found that, in particular with such a design of the bracket,optimum flow guidance can be achieved.

BRIEF DESCRIPTION OF THE DRAWING

An exemplary embodiment of the invention is shown in the drawing withreference to a moving blade of the exhaust-gas turbine of aturbocharger. In the drawing:

FIG. 1 shows a pressure-side side view of the moving blade;

FIG. 2 shows a section through the moving blade along line II—II in FIG.1;

FIG. 3 shows a section through the moving blade along line III—III inFIG. 1.

Only the elements essential for the understanding of the invention areshown. Elements not shown are, for example, the other components of theexhaust-gas turbine, including the blade shroud.

DETAILED DESCRIPTION OF THE INVENTION

The turbine blade shown in FIG. 1 and designed as a moving blade 1consists of a blade root 2, a platform 3 and a blade body 4. Theplatforms of adjacent turbine blades of the turbine wheel (not shown)bear directly against one another and thus form the inner boundary ofthe flow duct, which is closed on the outside by a blade shroud(likewise not shown). The blade body 4 has a leading edge 5, a trailingedge 6, a suction side 7, a pressure side 8 and a blade tip 9 (FIG. 2).

In the region of the blade tip 9, a bracket 10 is arranged on thepressure side 8 of the blade body 4, this bracket 10 extending only overa section 11 of the entire pressure side 8. This section 11 is anintegral part of a surface region 13, enclosed by an imaginary chord 12,of the pressure side 8. To this end, the chord 12 bears against a firstpoint 14 in the region of the leading edge 5 of the blade body 4 andagainst a second point 15 in the region of the trailing edge 6 of theblade body 4. The section accommodating the bracket 10 is formed betweenand at a distance from the two points 14, 15. It is therefore smallerthan the surface region 13 enclosed by the chord 12 (FIG. 3).

Formed between the first point 14 and the bracket 10 is a distance a₁which corresponds approximately to the blade thickness d₁ in this regionof the blade body 4. Likewise, a distance a₂ is formed between thesecond point 15 and the bracket 10, and this distance a₂ in turncorresponds approximately to the blade thickness d₂ in this region ofthe blade body 4.

The bracket 10 has a maximum height h_(max) above the pressure side 8,which corresponds approximately to a blade thickness d₃ which is formedin a region of the blade body 4 which is adjacent to the bracket 10 butremote from the blade tip 9 (FIG. 2). The maximum height h_(max) isarranged at a distance b from the leading edge 5, this distance b lyingat 30 to 40% of the chord length l of the blade body 4 (FIG. 3).Starting from the maximum height h_(max), the height of the bracket 10decreases continuously both in the direction of the leading edge 5 andin the direction of the trailing edge 6 of the blade body 4. In thiscase, the height of the bracket 10 is reduced in both directions in sucha way that a wavelike outer contour is obtained over the chord length l.

Since the bracket 10 is formed only in a section 11 of the pressure side8 and is offset to the inside relative to the bearing points of thechord 12 on the pressure side 8, and since its height continuouslydecreases in the direction of both blade edges, both wedge angles of theturbine blade 1, i.e. both the leading angle ω₁ and the trailing angleω₂ can be kept small compared with the solutions disclosed by the priorart.

In operation, this acute blade geometry improves the incident flow inthe region of the leading edge 5 of the blade body 4 and thus reducesthe Mach numbers. Likewise on account of the acute blade geometry, thegeneration of wake zones is prevented in the region of the trailing edge6 of the blade body 4. In this way, a further improvement in efficiencycan be achieved, the requisite reduction in the gap losses still beingensured. In addition, optimum flow guidance can be achieved by thewavelike outer contour of the bracket 10.

In addition to the bracket 10 on the pressure side 8 of the blade body4, a bracket (not shown) may also be arranged on the suction side 7, asa result of which the risk of overflow is further reduced and, given anappropriate design, the flow guidance can also be improved in thisregion. Of course, such a bracket 10 may be used not only in movingblades but also in guide blades.

LIST OF DESIGNATIONS

1 Turbine blade, moving blade

2 Blade root

3 Platform

4 Blade body

5 Leading edge

6 Trailing edge

7 Suction side

8 Pressure side

9 Blade tip

10 Bracket

11 Section

12 Chord

13 Surface region

14 Point, first

15 Point, second

a₁ Distance

a₂ Distance

b Distance

d₁ Blade thickness of 4

d₂ Blade thickness of 4

d₃ Blade thickness of 4

h_(max) Maximum height of 10

l Chord length of 4

ω₁ Leading angle of 4

ω₂ Trailing angle of 4

What is claimed is:
 1. A turbine blade having a blade body which isprovided with a leading edge, a trailing edge, a suction side and apressure side and which has a blade tip, a bracket being arranged on thepressure side of the blade body in the region of the blade tip, whereinthe bracket is formed merely in a section of a surface region of thepressure side, the surface region being enclosed by an imaginary chordbearing against a first point of the pressure side of the blade body inthe region of the leading edge and against a second point of thepressure side of the blade body in the region of the trailing edge, thesection accommodating the bracket being formed between and at a distancefrom the two points, wherein a distance is formed between the firstpoint and the bracket and between the second point and the bracket, andthis distance corresponds approximately to a blade thickness in thecorresponding region of the blade body.
 2. The turbine blade as claimedin claim 1, wherein the bracket, starting from the leading edge, has amaximum height above the pressure side located in a region of 30 to 40%of the chord length of the blade body, the height of the bracketcontinuously decreasing both in the direction of the leading edge of theblade body and in the direction of the trailing edge of the blade body.3. The turbine blade as claimed in claim 1, wherein the bracket is ofwavelike design.
 4. A turbine blade having a blade body which isprovided with a leading edge, a trailing edge, a suction side and apressure side and which has a blade tip, a bracket being arranged on thepressure side of the blade body in the region of the blade tip, whereinthe bracket is formed merely in a section of a surface region of thepressure side, the surface region being enclosed by an imaginary chordbearing against a first point of the pressure side of the blade body inthe region of the leading edge and against a second point of thepressure side of the blade body in the region of the trailing edge, thesection accommodating the bracket being formed between and at a distancefrom the two points, wherein the bracket, starting from the leadingedge, has a maximum height above the pressure side located in a regionof 30 to 40% of the chord length of the blade body, the height of thebracket continuously decreasing both in the direction of the leadingedge of the blade body and in the direction of the trailing edge of theblade body.